Eocene-aged basalts, north of Niksar (Tokat-Turkey), are quickly affected by chemical weathering, as well as physical and biological weathering. In order to assess the influence of chemical weathering on the engineering properties of these basalts, a study was performed in some profiles from the study area. The results of chemical analyses were used in various weathering indexes. These chemical indexes were compared with the petrographical weathering index and the microfracture density, in order to find the most suitable chemical index of weathering, applicable to basaltic rocks. The results suggest that the Parker Index and the loss on ignition can be used to find variations of the degree of chemical weathering in the basaltic rocks. In addition, physical and mechanical properties of the basalts were compared with the Parker Index and loss on ignition, and it was found that the dry density and the compressive strength decrease with weathering, while the porosity increases.